1. Field of the Invention
The present invention relates generally to an active suspension system for a vehicle having a plurality suspension units for maintaining a constant vehicle ride height. More particularly, the present invention relates to an active suspension system wherein the system controllers are integrated into the housing of the suspension unit.
2. Disclosure Information
Various types of active suspension systems have been proposed which are capable of responding to road inputs in real time with power inputs having sufficient robustness to control body motion of an automotive vehicle. As used herein, the term "active suspension" means a suspension which has a frequency response and power output characteristics sufficient to respond in real time to control force inputs to the vehicle chassis arising from such sources as road imperfections, crosswinds, and vehicle turning maneuvers. As used herein, the terms "body" and "chassis" mean either a conventional unitized automotive body or conventional frame and body automobile or any combination thereof. Active suspensions can be hydraulic systems wherein a hydraulic actuator in conjunction with complex valve componentry is used to maintain the ride and handling characteristics of the vehicle as well as the vehicle height at its optimum considerations. Other types of active suspension systems are electrically powered systems such those disclosed in U.S. Pat. Nos. 5,027,048; 5,060,959 both assigned to the assignee of the present invention, as well as U.S. Pat. Nos. 5,028,073; 4,969,662; and 4,892,328.
In the electrically powered systems described above, each includes a plurality of suspension units which are electrically connected to at least a system controller and typically to a power electronics module as shown in FIG. 1. The above systems disclose that the system controller, the power electronic module and other system modules operatively associated with the suspension units are located a discrete and remote distance away from the suspension unit itself. When the system controllers are located remote from the actuator motors themselves, disadvantages in the system can arise. For example, when the motor power drivers are located remote from the motor and when the motor power conditioning functions as either a brushless DC or as an AC drive, then the voltage present on the motor.leads will radiate considerable electro-magnetic interference (EMI). Prior attempts to alleviate the EMI include twisting the motor leads or providing a cable shield back to a suitable ground and/or slowing down the electrical transition starting switching. However, these methods and other methods to detune the switching events are at the expense of considerable loss in efficiency. Furthermore, locating the control modules distant from the individual suspension actuators can also lead to ripple currents outside of the actuator, increased noise pick-up as well as temperature induced disadvantage affects.
Therefore, it would be advantageous to provide a system wherein the system control modules are located as near as possible to the actuator itself. However, the functional integration of the system controllers and the motor power drivers for the suspension actuators has not been feasible to date for reasons of the thermal environments involved, the physical sizes of the components, especially passive devices, as well as the electrical environment of the system. The present invention overcomes these problems and provides a suspension unit for an electrically powered suspension system wherein the system controllers and the motor powered drivers are integrated directly into the suspension unit.